1. Field of the Invention
The invention-relates to a mask assembly for use in the delivery of Non-invasive Positive Airway Pressure (NPPV) for therapy of Sleep Disordered Breathing (SDB).
2. Background Information
The application of Continuous Positive Airway Pressure (CPAP) for therapy of Obstructive Sleep Apnea (OSA) was first taught by Sullivan in U.S. Pat. No. 4,944,310 (Sullivan). In CPAP treatment for OSA, pressurized air or other breathable gas is provided to the entrance of a patient""s airways at a pressure elevated above atmospheric pressure, typically in the range 4 to 20 cm H2O to xe2x80x9csplintxe2x80x9d open the patient""s airways and prevent obstructive apneas. Apparatus to deliver NPPV therapy typically comprises a blower, an air delivery conduit and a patient interface. The blower may be programmed to deliver a range of different forms of therapy.
In one form, a constant pressure of air or breathable gas is provided to the patient. It is also known for the level of treatment pressure to vary from breath to breath in accordance with patient need, that form of CPAP being known as automatically adjusting nasal CPAP treatment as described in U.S. Pat. No. 5,245,995 (Sullivan and Lynch). In another form, a relatively higher pressure of gas may be provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. In other modes, the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment. See, for example, U.S. Pat. No. 5,704,345 and International Publication Nos. WO98/12965 and WO99/61088, all of which are incorporated by reference herein. In this specification, the term NPPV therapy will be used to embrace all these forms of therapy.
The patient interface may take many forms, such as a nasal mask assembly, a nose and mouth mask assembly or nasal prongs assembly. A mask assembly typically, but not always, includes a rigid shell, a soft face-contacting cushion, a forehead support and headgear for securing the mask to the head.
In one known mask assembly, the headgear includes a cap portion with four straps. In use, the cap portion engages the occiput of the patient. Furthermore, in use, the two lower straps extend between the cap portion and a nasal mask while the two upper straps extend between the cap portion and a forehead support.
Some patient interfaces include quick release mechanisms. Since the patient must be able to sleep while wearing the patient interface, it must be comfortable. In addition, the patient interface must provide a good seal so any unintentional leak that occurs is minimized and any intentional leak is controlled. Since the shape of people""s noses, faces and heads vary widely, from a commercial perspective, it is important to be able to manufacture patient interfaces which can accommodate this range of facial shapes without carrying excessive inventory. A number of patient interfaces have been designed with the goals in mind of patient comfort, ease of use, adjustability and the ability to accommodate a wide range of patient face and head shapes.
U.S. Pat. No. 5,243,971 (Sullivan and Bruderer) provides a nasal mask which is suitable for use in CPAP or NPPV therapy. The mask has a face-contacting portion mounted to a shell which is sized and shaped to overfit the nose region of an intended wearer, and the face contacting portion is in the form of a distendable membrane which is molded from an elastomeric material. The distendable membrane and the shell together define a chamber, and pressurized gas admitted to the chamber causes the membrane to distend outwardly from the shell. When placed in contact with the face of the wearer, the distendable membrane is caused to overlay the covered facial regions and, under the influence of the pressurized gas, to conform three-dimensionally with the contours of the overlayed regions. An orifice is formed within the membrane and is shaped and positioned to admit gas from the chamber to the nasal passages of the wearer. The contents of this patent are hereby incorporated by cross-reference.
U.S. Pat. No. 6,112,746 (Kwok and Styles) describes a nasal cushion which comprises a substantially triangularly shaped frame from which extends a membrane. The frame has a scalloped edge by which the cushion is affixed to a mask body. The membrane has an aperture into which the wearer""s nose is received. The membrane is spaced away from the rim of the frame and its outer surface is of substantially the same shape as the rim. Respective notches receive the bridge of the wearer""s nose. The wearer""s nose is received through the aperture into the chamber within the mask body. The seal forming portion thus contacts both the surface of the wearer""s nose and a portion of the wearer""s face in the region between the base of the nose and the upper lip, and around the sides and over the bridge of the nose. The shape of the seal forming portion is particularly suited to effectively seal the difficult region of the facial contour that is the crease between the sides of the nose and the face. The contents of this patent are hereby incorporated by cross reference.
U.S. Pat. No. 6,119,693 (Kwok, Matchett and Grant) describes an adjustable forehead support for a nasal mask. An adjustable forehead support for a nasal or full-face mask is described wherein the forehead support may be adjusted for the different shapes and sizes of a facial profile. The forehead support utilizes a dual-arm system which adjusts the position of the forehead support vis-a-vis the mask and/or air flow tube. The angle of the mask to the face may be adjusted with the invention of the ""693 patent. The contents of that patent are hereby incorporated by cross-reference.
In international patent application PCT/AU00/00097 (WO 00/78384), a forehead support is disclosed that is adapted to be secured to a respiratory mask. The forehead support includes a joining member for securing to the mask and a cushion frame pivotally mounted to the joining member. The cushion frame is adapted to locate one or more forehead cushions. The cushion frame is also adapted to pivot relative to the joining member. In one form the cushion frame is also selectively lockable at two or more predetermined angular positions relative to the joining member. A respiratory mask assembly comprising a respiratory mask and a forehead support adapted to be secured to the mask is also disclosed. The contents of this specification are hereby incorporated by cross-reference.
Pending U.S. application Ser. No. 09/482,718 (Lithgow) describes headgear for securing a respiratory mask to a patient that incorporates a quick release arrangement. The headgear has at least one strap extending from each side of the mask, the straps being releasably fastened rearwards of the patient""s face to secure the mask. The headgear further includes release means in the form of a pull cord attached to an overlying strap at its region of fastening to the underlying strap and guided forward to be gripped at the front of patient. The contents of this specification are hereby incorporated by cross-reference.
A mask cushion for use with a mask assembly in NPPV therapy is disclosed in U.S. patent application Ser. No. 09/885,445, xe2x80x9cMask with Gussetxe2x80x9d to Frater et al. filed on Jun. 21, 2001 and assigned to the assignee of the present application, which application is incorporated by reference herein. The mask system disclosed therein includes a suspension mechanism to allow relative movement between a face-contacting cushion and a mask shell. The suspension mechanism also provides a predetermined force to the cushion that is a function of mask pressure, displacement of the cushion or both. In one embodiment of that invention, the mask cushion assembly includes an inflatable gusset acting as the suspension mechanism.
It has been a problem in the art to stabilize a mask frame (or shell) in a position over the user""s face so that the face-contacting side of the cushion is free to move relative to the frame-contacting side of the cushion while maintaining a seal. It is desirable to correct this problem in such a way that is comfortable for the patient and does not create excessive forces on the face of the user because of over-tightened straps.
In one aspect, the present invention discloses a head mount arrangement which is adapted to floatingly stabilize a mask frame in position without the use of a forehead support.
In another aspect, the present invention discloses a head mount arrangement which applies very small forces on the face through the mask frame until the mask is pressurized. In another aspect, the present invention discloses a force-passive or force-neutral mounting arrangement for a mask. In another aspect, a head mount arrangement is disclosed which allows adjustment of the angle and/or distance between the head mount and mask frame (or shell). In another aspect a method of stabilizing on a face a mask assembly comprising flexible straps and a semi-rigid head mount is provided, the method comprising positioning the head mount on a patients head, loosely adjusting the straps length and then applying pressure to the mask assembly.
An additional problem in the art has been that the cushion of a mask assembly is not easily attachable, removable and/or re-attachable to/from the shell. It is desirable for a user to be able to easily assemble, disassemble and/or reassemble the cushion and shell assembly for periodic cleaning and other miscellaneous purposes.
In one aspect, the present invention discloses a retaining ring which provides a secure, sealed connection between the cushion and the shell and is further easily disassembled from the shell for cleaning or other purposes.
An additional problem in the art occurs for a user of a respiratory mask to maintain a previously set strap adjustment position on the mask especially given the fact that it can be quite time consuming to correctly adjust strap positions on the mask. More particularly, in some respiratory mask assemblies, once the user had properly adjusted the mask and needed to remove the mask, there was no way to maintain the previously set positions.
In another aspect, the present invention discloses latching mechanisms which provide for a low-profile attachment between the shell of the mask and the harness and permit the mask to be to quickly, accurately and easily released and latched for use. Thus, the latching mechanisms allow the user to remove and reinstall the mask assembly and maintain the same preset strap adjustment.
The swivel and elbow arrangements of the prior art present problems for the air connections between a pressurized air source and the mask such as leakage around the elbow. The arrangements also suffer from tube drag which can cause the seal between the mask and user""s face to break. Some prior art swivel and elbow arrangements use and tight tolerances, which result in heavy friction in the movement of the ball and thus reduced mobility and flexibility of the elbow swivel joint. In another aspect, the mask assembly of the present invention includes a ball and socket joint for breathable air connection to the mask that reduces the effects of tube drag and provides increased flexibility between the air supply tube and the mask. In particular, the ball and socket joint of the present invention allows an air supply tube to be moved on an increased area of movement in comparison to the conventional elbow swivel joint.
In an embodiment of the present invention, the mask assembly includes a rigid shell, a cushion for attachment to the shell and a harness or headgear for attaching the cushion and shell to the patient (or user). The shell includes one or more latching mechanisms for attachment between the shell and the harness and for allowing the harness to be quickly, accurately and repeatedly tightened and untightened with respect to the user""s head while maintaining a preset harness length and fit. The latching mechanisms operate on an over center principle to quickly and easily be manipulated by the user (or a care-giver) from an open (or unlatched) position to a closed (or latched) position, and vice-versa.
The shell assembly further includes several features for improving the flow of gases (including air) through the mask and reducing noise levels associated with such gas flow. One such feature is the provision of exhalation ducts that direct the exhalation gas flow from an interior of the mask assembly to an exterior of the mask assembly in a flow direction alongside an air inlet tube to the mask. Another such feature is the provision of one or more baffles in an interior of the shell to direct and help keep separated the intake and exhalation gas flows.
The mask assembly also includes several features for quickly adjusting the fit of the mask assembly to the particular user to improve the sealing of the mask and the comfort of the user. Several different embodiments of adjustment mechanisms are disclosed, including mechanisms that can quickly and easily change the height and/or angle of a head mount with respect to the shell either simultaneously or independently of one another and mechanisms that can alter the fit of the connection between the shell assembly and the harness or headgear. In one embodiment of the present invention, the structure used for securing the shell/cushion assembly to the user""s head does not include a forehead support and does not contact the user""s forehead and also has the advantage of not leaving unsightly (though usually temporary) pressure marks on the user""s forehead as can other known masks.
In another embodiment, a ball and socket joint is provided that permits freedom of movement of a pressurized gas supply tube with respect to the mask assembly, thus preventing the movement of the gas supply tube from affecting the stability of the cushion and shell assembly and the integrity of the mask/face seal. The ball and socket joint may be positioned at some point in the air supply line to provide a highly flexible joint in the line for patient comfort.
Of course, portions of the aspects may form sub-aspects of the present invention. Also, various ones of the sub-aspects and/or aspects may be combined in various manners and also constitute additional aspects or sub-aspects of the present invention. These and other features and aspects of the present invention will be described in or be apparent from the detailed description below read in conjunction with the attached Figures, where like reference numerals indicate like components.